1. Field of the Invention
The present invention generally relates to an optical waveguide mounting member, a substrate, a semiconductor device, a method of manufacturing an optical waveguide mounting member, and a method of manufacturing a substrate, and more particularly to an optical waveguide mounting member, a substrate, a semiconductor device, a method of manufacturing an optical waveguide mounting member, and a method of manufacturing a substrate for transmitting optic signals to an optical element via an optic fiber.
2. Description of the Related Art
Development of optical communication is advancing along with the increases in speed and size of recent information communication. Ordinarily, in optical communication, electric signals are converted to optical signals, the optical signals are transmitted through an optic fiber, and the received optical signals are converted to electric signals by an optical element having a light emission and/or light reception part (hereinafter referred to as “light emission/reception part). The light emission/reception part is a part for transmitting and receiving optical signals. The optical element includes, for example, a vertical cavity surface emitting laser (VCSEL), a photodiode (hereinafter referred to as “PD”), and a laser diode (hereinafter referred to as “LD”).
In a semiconductor device having a substrate provided with the optical element, a core part of an optic fiber, which is mounted in a through-hole penetrating the substrate, is positioned in a manner facing the light emission/reception part of the optical element.
A conventional semiconductor device 10 including optical elements 15 and 16 is described with reference to FIG. 1. FIG. 1 is a cross-sectional view showing the semiconductor device 10 having the optical elements 15, 16. The semiconductor device 10 mainly includes a substrate 20, optical elements 15, 16 having light emission/reception parts 15A, 16A, an optical waveguide 17, and mirrors 21, 22.
The substrate 20 mainly includes a resin base material 11, through-holes 12a, 12b, an optic fibers 13, 14, and pads (not shown), wirings (not shown), and solder resist that covers the wirings (not shown). The pads, wirings, and the solder resist are provided on a plane 11A of the resin base material 11. The pads are provided for connecting to solder balls 24, 25 of the optical elements 15, 16. The pads are provided in an exposed state (i.e. not covered by the solder resist).
The through-holes 12a, 12b are formed in the resin base material 11 in a manner penetrating the resin base material 11 by irradiating a laser (e.g. a YAG laser, a CO2 laser, an excimer laser) to the resin base material 11. The through-hole 12a is provided with an optic fiber 13, and the through-hole 12b is provided with an optic fiber 14. The optic fibers 13, 14 include core parts 13a, 14a, and clad parts 13b, 14b that cover the core parts 13a, 14a. Optical signals are transmitted by the core parts 13a, 14a. 
The optical element 15, which is provided with the solder ball 24, has the solder ball 24 connected to the pad (not shown) of the substrate 20. Accordingly, optical element 15 is electrically connected to the substrate 20. The optical element 15 is mounted on the substrate 20 in a manner that the light emission/reception part 15A of the optical element 15 faces the core part 13a of the optic fiber 13.
The optical element 16, which is provided with the solder ball 25, has the solder ball 25 connected to the pad (not shown) of the substrate 20. Accordingly, optical element 16 is electrically connected to the substrate 20. The optical element 16 is mounted on the substrate 20 in a manner that the light emission/reception part 16A of the optical element 16 faces the core part 14a of the optic fiber 14.
The mirror 21 is provided at an end part 13B of the optic fiber 13 and the mirror 22 is provided at an end part 14B of the optic fiber 14. The mirrors 21, 22 are provided for enabling optical transmission between the optical waveguide 17 and the optic fibers 13, 14.
The optical waveguide 17 includes a core part 18 and a clad part 19 that covers the periphery of the core part 18. The optical waveguide 17 is provided between the mirror 21 and the mirror 22 for allowing optical signals to be transmitted therethrough (See, for example, Japanese Laid-Open Patent Application No. 2004-54003).
In the semiconductor 10, it is desirable to reduce deviation between the positions of the core parts 13a, 14a of the optic fibers 13, 14 (mounted in the through-holes 12a, 12b) and the positions of the corresponding light emission/reception parts 15A, 16A facing the core parts 13a, 13b, so that transmission loss between the optic fibers 13, 14 and the light emission/reception parts 15A, 16A can be reduced.
FIG. 2 is a plane view of the substrate 20 having the optic fiber 13 mounted in the through-hole 12a. In FIG. 2, L1 indicates a space formed between the wall of the through-hole 12a (12b) having a diameter R2 and an outer diameter R1 of the optical fiber 13 (14) (hereinafter referred to as “space L1”). However, in the semiconductor device 10, since the through-holes 12a, 12b corresponding to the optic fibers 13, 14 are formed by irradiating a laser (e.g. a YAG laser, a CO2 laser, an excimer laser) to the resin base material 11, it is difficult to form the through-holes 12a, 12b in a precise predetermined position in the resin base material 11, and it is difficult to control the size of the diameters of the through-holes 12a, 12b. 
Furthermore, since a large space L1 (e.g. approximately 10 μm) is provided between the wall of the through-hole 12a, 12b having diameter R2 and the optic fiber 13, 14 having outer diameter R1 for enabling attachment between the optic fibers 13, 14 and the through-holes 12a, 12b, the position of the core parts 13a, 14a of the optic fibers 13, 14 attached to the through-holes 12a, 12b tends to deviate from the position of the corresponding light emission/reception parts 15A, 16A. This makes it difficult to reduce transmission loss of optical signals.
Furthermore, even if the position between the core parts 13a, 14a and the light emission/reception parts 15A, 16A is optimized, the resin base material 11 in which the through-holes 12a, 12b are formed may change the position of the optic fibers 13, 14 attached to the through-holes 12a, 12b in a case where thermal deformation (thermal contraction or thermal expansion) of the resin base material 11 occurs when the temperature of the substrate 20 changes. This results in an increase of transmission loss of optical signals.
FIG. 3 shows an example a substrate having optic fibers in a state before being subjected to a polishing process. In FIG. 3, letters “A” and “B” each indicate a part of an optic fiber 36 protruding from a resin base material 331 (hereinafter referred to as “protruding part A” and “protruding part B”). With reference to FIG. 3, the process of polishing the protruding parts A, B is performed after pads 32, 37, wirings 33, 38, and solder resist 34, 39 are formed on both sides of the resin substrate 31. Therefore, the presence of the pads 32, 37, wirings 33, 38, and solder resist 34, 39 formed on both sides of the resin substrate 31 may obstruct the process of polishing the protruding parts A, B. Therefore, it is difficult to polish the protruding parts A, B of the optic fiber 36 with satisfactory precision in a direction perpendicularly intersecting with a plane direction of the resin substrate 31.